Revue Arachnologique, 2 (3)t 1979: 103-132. Comparative studies of Dictyna and Mallos (Araneae, Dictynidae) II. The relationship between courtship, mating, agression and cannibalism in species with differing types of social organization R.R. Jackson* (North Carolina Mental Health Research, P.O. Box 7532, Raleigh, North Carolina 27611) - I. Contents Résumé, summary. - . „ . 104 Introduction. ” ; . ; . .... 104 ' Methods and materials.. .............................. 107 Results. i . .... 107 L Elements of behavior. ..... 107 II. Organization of behavior during interactions in the laboratory. ,. 113 m . Mating in the laboratory. , . .. 115 IV. Observations from the natural habitats of the spiders. •. 117 V. Spinning behavior during courtship. ...... ... ... 117 . VI. The role of sexual dimorphism in communication. 117 VII. Aggression. ................................................................................................. 121 Vni. Spacing tendencies. ......................................................................... 123 IX. Cannibalism. ...................................................................................................... 124 Discussion.............................. ....................................................125 I. Interspecific differences in courtship. ' . 1 ...........................................125 II. Elements of behavior in other species........................... 126 III. The non-cannibalistic nature o f Mallos gregalis. ............................................ 126 IV. The non-aggressive nature of M allos gregalis ‘ .... 127 V. The function of courtship. .................................................................... 127 Acknowledgements..................... 129 References.......................................................................... 129 * Manuscrit reçu le 10 mai 1978; adresse actuelle de : Zoology Department, University of Canterbury, Christchurch 1, New Zealand. 104 R.R. Jackson Résumé L’organisation sodale chez les D icîyna et les Mallos comprend des espèces solitaires, des espèces qui vivent en groupes et gardent des territoires (grégaires, territoriales), et une espèce vivant en groupe (Mallos gregalis) qui ne conserve pas de territoires (grégaire, non- territoriale). Dans toutes les espèces, les mâles semblent être plus nomades que les fe­ melles; les femelles, plus sédentaires. Les femelles s’accouplent avec plusieurs males. Les dimorphismes sexuels des chélioères et des palpes pourraient être importants quant à leurs moyens de communiquer entre eux. Par contraste avec les autres espèces, le ML gregalis n’est pas agressif, il vit à proximité de ses voisins et n’est pas cannibale. La façon de faire la cour et l’accouplement varient selon les espèces et à l’intérieur même de ces dernières; cependant la façon de courtiser chez les espèces agressives et cannibales ne semble ni plus complexe ni plus circonspecte que celle des M. gregalis. Ces observations jettent un doûte sur l’hypothèse avancée précédemment que la principale fonction de faire la cour chez les araignées est de protéger les mâles contre les femelles cannibales. Sum m ary Social organization within D ictym and Mallos includes solitary spedes, species that live in groups and maintain territories (communal, territorial), and a group-living spedes (Mallos gregalis) that does not maintain territories (communal, non-territorial). In all spedes, males seem to be more nomadic; females, more sedentary. Females will mate with more than one male. Sexual dimorphisms of the chelicerae and pedipalps may be involved in communication. In contrast to other species,M. gregalis is non-aggressive, close-spacing, and non-cannibalistic. Courtship and mating behavior vary within and among spedes; however, the courtship of aggressive and cannibalistic spedes seems no more complex or cautious than that of M. gregalis. These observations bring into question the previously proposed hypothesis that a major function of courtship in spiders is to protect males from cannibalistic females. / V \ V- Introduction In spiders, cannibalism has repeatedly been given major importance, either expli- dtly or implicitly, in discussions concerning the function of courtship (e.g., BRISTOWE, 1958; BRISTOWE & LOCKET, 1926; GERHARDT & KAESTNER, 1937; KRAFFT, 1970; PLATNICK, 1971; SAVORY, 1928; TURNBULL, 1973; WITT, 1975). Spiders aie predators of arthropods, and the males of most species are within the size range of the prey of females. Observations in nature and espedally in the laboratory indicate that female spiders sometimes kill and feed on conspedfic males. Often the courtship behavior of males has a “cautious” appearance, with periods of approaching and withdrawing; and the female may rush toward the male in a manner appearing rather “violent”. Obser- Courtship and Dictynidae social organization 105 valions such these might seem to compel the conclusion that spider courtship behavior is largely the result of natural selection related to cannibalism. In other words, the func­ tion of courtship tends to be viewed as reducing the probability that the male will be treated as prey by the female. This will be called the “cannibalism reduction hypothesis" for the fonction of male courtship. Although the views of some authors tend to be complex, allowing for other functions in addition to cannibalism reduction, some varia­ tion of the cannibalism reduction hypothesis is a nearly ubiquitous element in discussions of spider courtship. Sometimes it is an explicitly proposed function; other times it is merely implied. The popular myth that female spiders usually prey on the males either during court­ ship or after copulation has been disclaimed many times by arachnologists. Sometimes the same arachnologists emphasize cannibalism reduction in discussions of the function of courtship. Perhaps cannibalism is not so frequent in spiders because of the effectiveness of courtship in preventing its occurrence, but this hypothesis needs critical investigation. Some observations on the behavior of dictynid spiders that are relevant to the cannibalism reduction hypothesis will be discussed here. These spiders are of special interest because different species live under differing types of social organization (JACK- SON, 1978a), and the cannibalistic tendencies of the species vary with their social orga­ nization. The majority of dictynids are solitary, each individual generally living alone in an individual web that does not touch other occupied webs. These are found especially on stems and leaves of shrubs and herbaceous plants. Mallos trivittatus Banks, D ictyna calcarata Banks, and D. albopUosa FranganiDo are communal and territorial, living in web complexes that consist of individual web units connected to each other by silk. Although several individuals often occupy a single web unit, generally two adults of the same sex or two immatures of comparable size do not share the same web unit. Each individual web and each web unit consists of a catching area and a nest in which the spiders tend to remain when not active or feeding. Mallos gregalis Simon is communal and non-territo­ rial, with hundreds of individuals sharing the same large communal webs which are not divided into web units. Females of M. trivittatus tend to be 7mm in body length; males 5mm. The other species in this study tend to be smaller; females approximately 5mm, males usually I 1™11 shorter. Species with differing types of social organization will be compared with respect to courtship, mating, aggression, and cannibalism. Courtship is defined as heterosexual communicatory behavior that forms the normal preliminaries to mating (JACKSON, 1977a); mating is used as synonym for copulation. WlLSON*s (1975) definition of com­ munication will be used: “Action on the part of one organism (or cell) that alters the probability pattern of behavior in another organism (or cell) in a fashion adaptive to either or both participants." Signals are behavioral and other characteristics of an orga­ nism used in communication (OTTE, 1974). Aggression is behavior of one individual that reduces the freedom or fitness of another individual (WILSON, 1975), with usage restric­ ted to intraspecific interactions for the present discussion. Cannibalism is intraspecific predation (FOX, 1975). Whether cannibalism is motivationally distinct from other forms of aggression (see HUNTINGFORD, 1976;MOYER, 1968) has not been determined for these spiders. 106 R.R. Jackson Fig. 1. — Maintenance cage constructed from clear plastic petri dish (diameter: 9 cm). Diameter of all holes: I e”1. a: Hole plugged with cork, b: Hole covered by metal screen, for ventilation, c: Cotton roll (4cmx Ie®) inserted through hole. Opposite end set in glass jar (d) containing water, providing continual moisture to interior of cage, e: Culture of Drosophila melanogaster in glass vial, f: Plastic cap with hole, g: Plastic tube inserted at one end through hole in lid of culture vial and at other end through hole in cage. Flies emerge from culture and travel through tube into cage, providing continual food for spiders. Fresh culture vials substituted as neoes- sary. Courtship and Dictynidae social organization 107 Methods and materials General methodology will be described here. Specific methods used in studies of spacing and cannibalism will be given in the appropriate sections. In the laboratory. At gregalis in large communal webs were maintained on a diet of houseflies [Musca domestica), provided at approximately 5-day intervals. Temperature